Cell carriers experiencing heavy call volume in Boston

Crystal Davis, a Sprint spokeswoman, said, "Minus some mild call blocking on our Boston network due to increased traffic, our service is operating normally."

In a statement, Verizon said it is adding network capacity to handle increased cellphone traffic. 

"There was no damage to the Verizon Wireless network, which is seeing elevated calling and data usage throughout the region since the explosions occurred," Verizon said.

AT&T said its customers may experience problems with voice and data services because of the spike in traffic. The company advised that people text for emergencies and limit non-emergency calls.

T-Mobile said that it increased capacity ahead of the marathon and its network "continues to perform well."

At least 2 people were killed and 23 were injured in explosions at the finish line of the Boston Marathon, according to police.

NBC News reported that small home-made bombs were responsible for the blasts. Intelligence officials said two more explosive devices were found and that authorities had begun dismantling them.  

Last year, the FCC asked for public input on whether and when local police should be allowed to cut off cellphone service. 

The agency noted that that there are risks involved in blocking wireless access, such as preventing people from being able to call 911. But the commission also acknowledged that cellphones could be used to detonate bombs or to coordinate violent mobs. 

— Last updated at 7:00 p.m.